
<template>
  <ul class="list">
    <li class="item"
        v-for="item of letters" :key="item" :ref="item" @touchstart="handleTouchStart" @touchmove="handleTouchMove" @touchend="handleTouchEnd" @click="handleLetterClick"
    >{{item}}</li>
  </ul>
</template>

<script>
  export default {
    name:'CityAlphabet',
    props:{
      cities:Object
    },
    computed:{
      letters () {
        const letters =[]
        for(let i in this.cities){
          letters .push(i)
        }
        return letters
      }
    },
    data (){
      return {
        touchStatus:false,
        starY:0,
        timer:null
      }
    },
    updated (){
      this.statusY = this.$refs['A'][0].offsetTop
    },
    methods:{
      handleLetterClick(e){
        this.$emit('change',e.target.innerText);
      },
      handleTouchStart(){
        this.touchStatus = true
      },
      handleTouchMove(e){
        //滑动旁边的字母表 列表跟着滚动。
        if(this.touchStatus){
          if(this.timer){
            clearTimeout(this.timer)
          }
          this.timer = setTimeout(() =>{
            const touchY = e.touches[0].clientY - 79;
            const index = Math.floor((touchY - this.statusY)/20);
            if(index >= 0 && index < this.letters.length){
              this.$emit('change',this.letters[index])
            }
          },16)
        }
      },
      handleTouchEnd(){
        this.touchStatus = false
      }
    }
  }
</script>

<style lang="stylus" scoped>
  @import "~styles/varibles.styl"
  .list
    display :flex
    position :absolute
    flex-direction :column
    justify-content :center
    top:1.58rem
    right:0
    bottom:0
    width :.4rem
    .item
      line-height :.4rem
      color:$bgColor
      text-align :center
</style>
